Method and apparatus for transmitting wake-up packet in wireless lan system

ABSTRACT

Disclosed are a method and apparatus for transmitting a wake-up packet in a wireless LAN system. Specifically, a transmission apparatus composes a wake-up packet and transmits same to a receiving apparatus. An OOK scheme and Manchester coding are applied to the wake-up packet. The wake-up packet comprises a sequence containing first information and second information. The first information and second information comprise on and off signals. The on signal applies a first sequence on K number of successive subcarriers in a 20 MHz band, and is transmitted by means of a first symbol generated by carrying out a 64-point IFFT. In the first sequence, one from among a subcarrier having a subcarrier index that is an even number and subcarrier having a subcarrier index that is an odd number is nulled.

BACKGROUND OF THE INVENTION Field of the Invention

This specification relates to a method for performing low powercommunication in a wireless LAN (WLAN) system and, most particularly, toa method and apparatus for transmitting a wake-up packet by applying anOOK scheme and Manchester coding in a wireless LAN (WLAN) system.

Related Art

Discussion for a next-generation wireless local area network (WLAN) isin progress. In the next-generation WLAN, an object is to 1) improve aninstitute of electronic and electronics engineers (IEEE) 802.11 physical(PHY) layer and a medium access control (MAC) layer in bands of 2.4 GHzand 5 GHz, 2) increase spectrum efficiency and area throughput, 3)improve performance in actual indoor and outdoor environments such as anenvironment in which an interference source exists, a denseheterogeneous network environment, and an environment in which a highuser load exists, and the like.

An environment which is primarily considered in the next-generation WLANis a dense environment in which access points (APs) and stations (STAs)are a lot and under the dense environment, improvement of the spectrumefficiency and the area throughput is discussed. Further, in thenext-generation WLAN, in addition to the indoor environment, in theoutdoor environment which is not considerably considered in the existingWLAN, substantial performance improvement is concerned.

In detail, scenarios such as wireless office, smart home, stadium,Hotspot, and building/apartment are largely concerned in thenext-generation WLAN and discussion about improvement of systemperformance in a dense environment in which the APs and the STAs are alot is performed based on the corresponding scenarios.

In the next-generation WLAN, improvement of system performance in anoverlapping basic service set (OBSS) environment and improvement ofoutdoor environment performance, and cellular offloading are anticipatedto be actively discussed rather than improvement of single linkperformance in one basic service set (BSS). Directionality of thenext-generation means that the next-generation WLAN gradually has atechnical scope similar to mobile communication. When a situation isconsidered, in which the mobile communication and the WLAN technologyhave been discussed in a small cell and a direct-to-direct (D2D)communication area in recent years, technical and business convergenceof the next-generation WLAN and the mobile communication is predicted tobe further active.

SUMMARY OF THE INVENTION Technical Objects

This specification proposes a method and apparatus for transmitting awake-up packet by applying an OOK scheme and Manchester coding in awireless LAN (WLAN) system.

Technical Solutions

An example of this specification proposes a method and device fortransmitting a wake-up packet in a wireless LAN system.

The exemplary embodiment of this specification may be performed by thetransmitting device. And, a receiving device may correspond to alow-power wake-up receiver, and the transmitting device may correspondto an AP.

Firstly, the terms will be defined. An ON-signal may correspond to asignal having an actual power value. An OFF-signal may correspond to asignal that does not have an actual power value. A first information maycorrespond to Information 0, and a second information may correspond toInformation 1.

The transmitting device generates a wake-up packet.

The transmitting device transmits the wake-up packet to the receivingdevice.

The generation process of the wake-up packet will hereinafter bedescribed in detail.

An On-Off Keying (OOK) scheme and Manchester coding are applied in thewake-up packet. Accordingly, the wake-up packet includes a sequencebeing configured of the first information and the second information.

The first information and the second information are configured of anON-signal and an OFF-signal. More specifically, the first informationmay be configured in an order of an ON-signal and an OFF-signal. And,the second information may be configured in an order of an OFF-signaland an ON-signal. The ON-signal may indicate 1, and the OFF-signal mayindicate 0. Accordingly, the first information may be indicated as 10,and the second information may be indicated as 01. This indicates/isrelated with that Manchester coding is applied, and, accordingly, atransition in the signal magnitude occurs at a mid-point of a symbol.

In the first information and the second information, the order of theON-signal and the OFF-signal may also be changed. More specifically, thefirst information may be indicated as 01, and the second information maybe indicated as 10. However, the exemplary embodiment of thisspecification is described based on an assumption that the firstinformation indicates/is related with 10, and that the secondinformation indicates/is related with 01.

Additionally, each of the first information and the second informationcorrespond to a 1-bit information.

Additionally, the ON-signal may correspond to a signal given a powervalue of beta*ones(1,K). The OFF-signal may correspond to a signal givena power value of zeros(1,K). The beta is a power normalization factor.More specifically, the transmitting device may know, in advance, thepower values of the ON-signal and the OFF-signal and may configure thefirst information and the second information accordingly. By using anenvelope detector for decoding the first information and the secondinformation, the receiving device may reduce the amount of power that isconsumed when performing the decoding process.

The ON-signal is transmitted through a first symbol, which is generatedby applying a first sequence on K number of consecutive subcarriers of a20 MHz band and by performing 64-point Inverse Fast Fourier Transform(IFFT). More specifically, the ON-signal may be transmitted through asymbol, which is generated by performing IFFT on one bit. At this point,K is an integer.

In the first sequence, one of a subcarrier having an even-numberedsubcarrier index and a subcarrier having an odd-numbered subcarrierindex is nulled. More specifically, if a subcarrier having aneven-numbered subcarrier index is nulled in the first sequence, thesubcarrier having an odd-numbered subcarrier index may have acoefficient of 1 or -1. More specifically, the subcarrier having theodd-numbered subcarrier index may have a coefficient.

Alternatively, if a subcarrier having an odd-numbered subcarrier indexis nulled in the first sequence, the subcarrier having an even-numberedsubcarrier index may have a coefficient of 1 or -1. More specifically,the subcarrier having the even-numbered subcarrier index may have acoefficient.

More specifically, in the first sequence, a coefficient may exist at aninterval of two spaces of subcarrier indexes.

Additionally, the OFF-signal may be transmitted through a second symbol,which is generated by applying a second sequence to K number ofconsecutive subcarriers of a 20 MHz band and by performing 64-pointIFFT. In the second sequence, the coefficients of all subcarriers areset to 0.

The K number of subcarriers may correspond to a partial band of the 20MHz band. For example, when it is assumed that K=13, and that 20 MHzcorresponds to/is related with the reference band, even though 64subcarriers (or bit sequences) may be used, only 13 subcarriers aresampled and processed with IFFT. Accordingly, the 13 subcarriers maycorrespond to approximately 4.06 MHz. More specifically, a specificsequence (first sequence or second sequence) is configured only in the13 subcarriers, which are selected as a sample, and the remainingsubcarriers excluding the 13 subcarriers are all set to 0. Morespecifically, in the frequency domain, it may be understood that thepower exists for only 4.06 MHz of the 20 MHz band.

Additionally, the subcarrier spacing between each of the K number ofsubcarriers may correspond to 312.5 KHz.

Since the transmitting device performs IFFT after applying a firstsequence having a coefficient at an interval of two subcarrier indexspaces to K number of subcarriers, a 3.2 us-length signal having a cycleof 1.6 us is generated. Accordingly, each of the first symbol and thesecond symbol may have a length of 1.6 us. More specifically, each ofthe first symbol and the second symbol may correspond to a sub-symbol ofa symbol, which is generated by performing IFFT.

Moreover, by inserting a cyclic prefix (CP) in front of each symbol, theoccurrence of Inter Symbol Interference (ISI) may be reduced orprevented.

For example, the first information may be transmitted by having a firstcyclic prefix (CP) inserted only in front of the first symbol.Alternatively, the first information may be transmitted by having asecond CP inserted in front of the first symbol and a third CP insertedin front of the second symbol. Herein, the first CP may have length of0.8 us, and the second CP and the third CP may each have a length of 0.4us. More specifically, in the former case, a long CP is inserted isinserted in the foremost part of the signal, and, in the latter case,short CPs are inserted at the front and in the middle of the signal(i.e., a short CP is inserted in front of each sub-symbol). The formercase is effective in case the influence of the ISI is large at theforemost part of the signal, and the latter case is effective in casethe influence of the ISI also exists in the mid-portion of the signal.

As another example, the second information may be transmitted by havinga first CP inserted only in front of the second symbol. Alternatively,the second information may be transmitted by having a second CP insertedin front of the second symbol and a third CP inserted in front of thefirst symbol. Herein, the first CP may have length of 0.8 us, and thesecond CP and the third CP may each have a length of 0.4 us. Similarly,in the former case, a long CP is inserted is inserted in the foremostpart of the signal, and, in the latter case, short CPs are inserted atthe front and in the middle of the signal (i.e., a short CP is insertedin front of each sub-symbol). The former case is effective in case theinfluence of the ISI is large at the foremost part of the signal, andthe latter case is effective in case the influence of the ISI alsoexists in the mid-portion of the signal.

As yet another example, the first information may be transmitted byhaving a first CP inserted in front of the first symbol and a second CPinserted in front of the second symbol. The second information may betransmitted by having the first CP inserted in front of the secondsymbol and the second CP inserted in front of the first symbol. Each ofthe first CP and the second CP may have a length of 0.8 us. According tothe above-described exemplary embodiment, a long CP may be inserted infront of each sub-symbol, thereby enhancing the effect of reducing theISI.

Effects of the Invention

According to an example of this specification, by having a transmittingdevice transmit a wake-up packet after generating the wake-up packet byapplying an OOK modulation method, a receiving device may reduce powerconsumption by using an envelope detector when performing wake-updecoding. Accordingly, the receiving device may decode the wake-uppacket with minimum power. Accordingly, since the transmitting devicealso generates the wake-up packet by applying Manchester coding,consecutive occurrence of Off symbols may be prevented. Thus, theproblem of coexistence with the legacy Wi-Fi device may be resolved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN).

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

FIG. 4 is a diagram illustrating a low-power wake-up receiver in anenvironment where data is not received.

FIG. 5 is a diagram illustrating a low-power wake-up receiver in anenvironment where data is received.

FIG. 6 illustrates an example of a wake-up packet structure according toan exemplary embodiment of this specification.

FIG. 7 illustrates a signal waveform of a wake-up packet according to anexemplary embodiment of this specification.

FIG. 8 illustrates a diagram for describing a principle for determiningconsumed power in accordance with a ratio between bit value 1 and 0 thatconfigure information of a binary sequence format by using the OOKscheme.

FIG. 9 illustrates a method for designing an OOK pulse according to anexemplary embodiment of this specification.

FIG. 10 is a descriptive diagram of a Manchester coding method accordingto an exemplary embodiment of this specification.

FIG. 11 illustrates an example of inserting a CP in a symbol adoptingManchester coding according to an exemplary embodiment of thisspecification.

FIG. 12 illustrates another example of inserting a CP in a symboladopting Manchester coding according to an exemplary embodiment of thisspecification.

FIG. 13 is a flow chart showing a procedure of transmitting a signalafter applying the OOK scheme and Manchester coding according to anexemplary embodiment of this specification.

FIG. 14 is a block view illustrating a wireless device to which theexemplary embodiment of the present invention can be applied.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

FIG. 1 is a conceptual view illustrating the structure of a wirelesslocal area network (WLAN).

An upper part of FIG. 1 illustrates the structure of an infrastructurebasic service set (BSS) of institute of electrical and electronicengineers (IEEE) 802.11.

Referring the upper part of FIG. 1, the wireless LAN system may includeone or more infrastructure BSSs (100, 105) (hereinafter, referred to asBSS). The BSSs (100, 105) as a set of an AP and an STA such as an accesspoint (AP) (125) and a station (STA1) (100-1) which are successfullysynchronized to communicate with each other are not concepts indicatinga specific region. The BSS (105) may include one or more STAs (105-1,105-2) which may be joined to one AP (130).

The BSS may include at least one STA, APs (125, 130) providing adistribution service, and a distribution system (DS) (110) connectingmultiple APs.

The distribution system (110) may implement an extended service set(ESS) (140) extended by connecting the multiple BSSs (100, 105). The ESS(140) may be used as a term indicating one network configured byconnecting one or more APs (125, 230) through the distribution system(110). The AP included in one ESS (140) may have the same service setidentification (SSID).

A portal (120) may serve as a bridge which connects the wireless LANnetwork (IEEE 802.11) and another network (e.g., 802.X).

In the BSS illustrated in the upper part of FIG. 1, a network betweenthe APs (125, 130) and a network between the APs (125, 130) and the STAs(100-1, 105-1, 105-2) may be implemented. However, the network isconfigured even between the STAs without the APs (125 and 130) toperform communication. A network in which the communication is performedby configuring the network even between the STAs without the APs (125,130) is defined as an Ad-Hoc network or an independent basic service set(IBSS).

A lower part of FIG. 1 illustrates a conceptual view illustrating theIBSS.

Referring to the lower part of FIG. 1, the IBSS is a BSS that operatesin an Ad-Hoc mode. Since the IBSS does not include the access point(AP), a centralized management entity that performs a managementfunction at the center does not exist. That is, in the IBSS, STAs(150-1, 150-2, 150-3, 155-4, 155-5) are managed by a distributed manner.In the IBSS, all STAs (150-1, 150-2, 150-3, 155-4, 155-5) may beconstituted by movable STAs and are not permitted to access the DS toconstitute a self-contained network.

The STA as a predetermined functional medium that includes a mediumaccess control (MAC) that follows a regulation of an Institute ofElectrical and Electronics Engineers (IEEE) 802.11 standard and aphysical layer interface for a radio medium may be used as a meaningincluding all of the APs and the non-AP stations (STAs).

The STA may be called various a name such as a mobile terminal, awireless device, a wireless transmit/receive unit (WTRU), user equipment(UE), a mobile station (MS), a mobile subscriber unit, or just a user.

Meanwhile, the term user may be used to indicate diverse meanings. Forexample, the term user may be used to refer to an STA participating inan uplink MU MIMO and/or uplink OFDMA transmission in a wireless LAN(WLAN) communication. However, the usage of this term will not belimited only to this.

FIG. 2 is a diagram illustrating an example of a PPDU used in an IEEEstandard.

As illustrated in FIG. 2, various types of PHY protocol data units(PPDUs) may be used in a standard such as IEEE a/g/n/ac, etc. In detail,LTF and STF fields include a training signal, SIG-A and SIG-B includecontrol information for a receiving station, and a data field includesuser data corresponding to a PSDU.

In the embodiment, an improved technique is provided, which isassociated with a signal (alternatively, a control information field)used for the data field of the PPDU. The signal provided in theembodiment may be applied onto high efficiency PPDU (HE PPDU) accordingto an IEEE 802.11ax standard. That is, the signal improved in theembodiment may be HE-SIG-A and/or HE-SIG-B included in the HE PPDU. TheHE-SIG-A and the HE-SIG-B may be represented even as the SIG-A andSIG-B, respectively. However, the improved signal proposed in theembodiment is not particularly limited to an HE-SIG-A and/or HE-SIG-Bstandard and may be applied to control/data fields having various names,which include the control information in a wireless communication systemtransferring the user data.

FIG. 3 is a diagram illustrating an example of an HE PDDU.

The control information field provided in the embodiment may be theHE-SIG-B included in the HE PPDU. The HE PPDU according to FIG. 3 is oneexample of the PPDU for multiple users and only the PPDU for themultiple users may include the HE-SIG-B and the corresponding HE SIG-Bmay be omitted in a PPDU for a single user.

As illustrated in FIG. 3, the HE-PPDU for multiple users (MUs) mayinclude a legacy-short training field (L-STF), a legacy-long trainingfield (L-LTF), a legacy-signal (L-SIG), a high efficiency-signal A(HE-SIG A), a high efficiency-signal-B (HE-SIG B), a highefficiency-short training field (HE-STF), a high efficiency-longtraining field (HE-LTF), a data field (alternatively, an MAC payload),and a packet extension (PE) field. The respective fields may betransmitted during an illustrated time period (that is, 4 or 8 us).

A PPDU that is used in the IEEE standard is described as a PPDUstructure being transmitting mainly within a channel bandwidth of 20MHz. A PPDU structure that is transmitted within a bandwidth (e.g., 40MHz, 80 MHz) that is wider than the channel bandwidth of 20 MHz maycorrespond to a structure applying linear scaling of the PPDU structurebeing used in the channel bandwidth of 20 MHz.

The PPDU that is used in the IEEE standard is generated based on a 64Fast Fourier Transform (FFT), and a cyclic prefix (CP) portion maycorrespond to 1/4. In this case, the length of a valid (or effective)symbol section (or FFT section) may be equal to 3.2 us, a CP length maybe equal to 0.8 us, and a symbol duration may be equal to 4 us (=3.2us+0.8 us), which corresponds to/is related with a sum of the length ofthe valid symbol section and the CP length.

A wireless network is ubiquitous, and the wireless network is generallyinstalled indoors but is also often installed outdoors. The wirelessnetwork transmits and receives information by using diverse techniques.For example, although the wireless network will not be limited only tothis, two of the most broadly supplied techniques that are used forcommunication correspond to an IEEE 802.11n standard and an IEEE802.11ac standard, which follow the IEEE 802.11 standard.

The IEEE 802.11 standard designates a common Medium Access Control (MAC)layer, which provides diverse functions for operating the IEEE 802.11based wireless LAN (WLAN). The MAC layer controls access of sharedradio, and, by using a protocol that enhances communication through aradio medium, the MAC layer manages and maintains communication betweenIEEE 802.11 stations (e.g., a wireless network card (NIC) of a personalcomputer (PC), another wireless device or stations (STA), and an accesspoint (AP)).

As the next new product of the 802.11ac, IEEE 802.11ax was proposed inorder to enhance efficiency of a WLAN network, most particularly, inhigh-density regions, such as public hotspots and other high-trafficregions. Additionally, the IEEE 802.11 may also use orthogonal frequencydivision multiple access (OFDMA). A High Efficiency WLAN study group(HEW SG) within an IEEE 802.11 Work Group considers an enhancement inspectrum efficiency in order to enhance the system throughput/surface ina high-density scenario of an access point (AP) and/or station (STA).

Although small computing devices, such as wearable devices, sensors,mobile devices, and so on, are restricted due to their compact batterycapacity, small computing devices support wireless communicationtechniques, such as Wi-Fi, Bluetooth®, Bluetooth® Low Energy (BLE), andso on, and, then, the small computing devices should exchange data bybeing connected to other computing devices, such as smart phones,tablets, personal computers, and so on. Since such communicationconsumes power, it is important to minimize power consumption of suchcommunication. One of the most ideal strategies for minimizing powerconsumption is to maintain data transmission and reception withoutexcessively increasing delay (or latency) and to turn off the power forcommunication blocks as frequently as possible. More specifically, acommunication block is transmitted immediately before data reception,and the communication block is turned on only when data that needs to bewoken up exists, and, during the rest of the time, the power of thecommunication block is turned off.

Hereinafter, a Low-Power Wake-Up Receiver (LP-WUR) will be described indetail.

The communication system (or communication sub-system) that is describedin this specification includes a main radio (802.11) and a low-powerwake-up receiver.

The main radio is used for the transmission and reception of user data.The main radio is turned off when there is no data or packet that is tobe transmitted. The low-power wake-up receiver wakes up the main radiowhen there is a packet that is to be received. At this point, the userdata is transmitted and received by the main radio.

The low-power wake-up receiver is not used (or provide) for the userdata. The low-power wake-up receiver corresponds to/is related with areceiver for simply waking up the main radio. More specifically, thelow-power wake-up receiver does not include a transmitter. The low-powerwake-up receiver is activated while the main radio is turned off. Duringits activated state, the low-power wake-up receiver aims to achieve itstarget power consumption of less than 1 mW. Additionally, the low-powerwake-up receiver uses a narrow band of less than 5 MHz. Furthermore, atarget transmission range of the low-power wake-up receiver is the sameas a target transmission range of the legacy 802.11.

FIG. 4 is a diagram illustrating a low-power wake-up receiver in anenvironment where data is not received. FIG. 5 is a diagram illustratinga low-power wake-up receiver in an environment where data is received.

As shown in FIG. 4 and FIG. 5, in case data that is to be transmittedand received exists, one of the methods for implementing the most idealtransmission and reception strategy is to add a low-power wake-upreceiver (LP-WUR) that is capable of waking up a main radio, such asWi-Fi, Bluetooth® radio, Bluetooth® Low Energy (BLE) radio, and so on.

Referring to FIG. 4, the Wi-Fi/BT/BLE radio (420) is turned off, and thelow-power wake-up receiver (430) is turned on in a state where data isnot received. According to part of the related studies, the powerconsumption of such low-power wake-up receiver (LP-WUR) may be less than1 mW.

However, as shown in FIG. 5, if a wake-up packet is received, thelow-power wake-up receiver (530) wakes up the entire (or whole)Wi-Fi/BT/BLE radio (520) so that a data packet following the wake-uppacket can be accurately received. However, in some cases, actual dataor an IEEE 802.11 MAC frame may be included in the wake-up packet. Inthis case, although the entire Wi-Fi/BT/BLE radio (520) cannot be wokenup, the necessary process should be carried out by waking up only partof the Wi-Fi/BT/BLE radio (520). This may result in a considerableamount of power saving.

An exemplary technique that is described in this specification defines amethod of a segmented wake-up mode for a Wi-Fi/BT/BLE radio using alow-power wake-up receiver. For example, actual data being included in awake-up packet may be directly delivered to a memory block withoutwaking up the Wi-Fi/BT/BLE radio.

As another example, in case an IEEE 802.11 MAC frame is included in thewake-up packet, only a MAC processor of the Wi-Fi/BT/BLE wireless device(or radio) needs to be woken up in order to process the IEEE 802.11 MACframe, which is included in the wake-up packet. More specifically, thepower of a PHY module of the Wi-Fi/BT/BLE radio may be turned off ormaintained in a low-power mode.

Since a plurality of segmented wake-up modes for a Wi-Fi/BT/BLE radiousing a low-power wake-up receiver are defined, when a wake-up packet isreceived, the power of the Wi-Fi/BT/BLE radio must be turned on.However, according to the exemplary embodiment of this specification,only a necessary (or required) part (or configuration element) of theWi-Fi/BT/BLE radio may be selectively woken up, thereby saving a largeramount of energy and reducing stand-by (or waiting) time. A large numberof solutions using the pow-power wake-up receiver wakes up the entireWi-Fi/BT/BLE radio when receiving a wake-up packet. According to anexemplary aspect that is discussed in this specification, since only apart (or element) of the Wi-Fi/BT/BLE radio that is required forprocessing the receiving data is woken up, a considerable amount ofenergy is saved, and unnecessary stand-by (or waiting) time that isneeded for waking up the main radio may be reduced.

Additionally, according to this exemplary embodiment, the low-powerwake-up receiver (530) may wake up the main radio (520) based on thewake-up packet that is transmitted from a transmitting device (500).

Furthermore, the transmitting device (500) may be configured to transmitthe wake-up packet to a receiving device (510). For example, thetransmitting device (500) may instruct the low-power wake-up receiver(530) to wake up the main radio (520).

FIG. 6 illustrates an example of a wake-up packet structure according toan exemplary embodiment of this specification.

A wake-up packet may include one or more legacy preambles. One or morelegacy devices may decode or process the legacy preamble(s).

Additionally, the wake-up packet may include a payload after a legacypreamble. The payload may be modulated by using a simple modulationscheme, e.g., an On-Off Keying (OOK) scheme.

Referring to FIG. 6, the transmitting device may be configured togenerate and/or transmit a wake-up packet (600). And, the receivingdevice may be configured to process the received wake-up packet (600).

Additionally, the wake-up packet (600) may include a legacy preamble,which is defined by the IEEE 802.11 specification, or another randompreamble (610). And, the wake-up packet (600) may also include a payload(620).

A legacy preamble provides a coexistence with a legacy STA. The legacypreamble (610) for the coexistence uses an L-SIG field for protectingthe packet. Through the L-SIG field within the legacy preamble (610), an802.11 STA may detect a beginning (or a start point) of the legacypreamble (610). And, through the L-SIG field within the legacy preamble(610), the 802.11 STA may know (or acknowledge) an end (or last part) ofthe packet. Additionally, by adding a symbol that is modulated by usingBPSK after the L-SIG, a false alarm of an 802.11n terminal (or device)may be reduced. A symbol (4 us) that is modulated by using BPSK also hasa 20 MHz bandwidth, just as the legacy part. The legacy preamble (610)corresponds to/is related with a field for a third party legacy STA (anSTA not including an LP-WUR). The legacy preamble (610) is not decodedby the LP-WUR.

The payload (620) may include a wake-up preamble (622). The wake-uppreamble (622) may include a sequence of bits that are configured toidentify the wake-up packet (600). The wake-up preamble (622) may, forexample, include a PN sequence.

Additionally, the payload (620) may include a MAC header (624) includingaddress information of a receiving device, which receives the wake-uppacket (600), or an identifier of the receiving device.

Additionally, the payload (620) may include a frame body (626), whichmay include other information of the wake-up packet. For example, lengthor size information of the payload may be included in the frame body(626).

Furthermore, the payload (620) may include a frame check sequence (FCS)field (628) including a cyclic redundancy check (CRC) value. Forexample, the FCS field (628) may include a CRC-8 value or a CRC-16 valueof the MAC header (624) and the frame body (626).

FIG. 7 illustrates a signal waveform of a wake-up packet according to anexemplary embodiment of this specification.

Referring to FIG. 7, a wake-up packet (700) includes a legacy preamble(802.11 preamble (710) and a payload being modulated by OOK. In otherwords, the wake-up packet (700) is configured of a format in which alegacy preamble and a new LP-WUR signal waveform coexist.

Additionally, the legacy preamble (710) may be modulated in accordancewith an OFDM modulation scheme. More specifically, the OOK scheme is notapplied to the legacy preamble (710). Conversely, the payload may bemodulated in accordance with the OOK scheme. However, a wake-up preamble(722) within the payload may be modulated in accordance with a differentmodulation scheme.

If the legacy preamble (710) is transmitted within a channel bandwidthof 20 MHz in which 64 FFT is applied, the payload may be transmittedwithin a channel bandwidth of approximately 4.06 MHz. This will bedescribed in more detail in the following description of an OOK pulsedesigning method.

Firstly, a modulation method using the OOK scheme and a Manchestercoding method will be described in detail.

FIG. 8 illustrates a diagram for describing a principle for determiningconsumed power in accordance with a ratio between bit value 1 and 0 thatconfigure information of a binary sequence format by using the OOKscheme.

Referring to FIG. 8, information of a binary sequence format having 1 or0 as the bit values is expressed in the drawing. By using such bitvalues of 1 or 0 of the binary sequence format information, an OOKmodulation scheme communication may be carried out. More specifically,by considering the bit values of the binary sequence format information,the OOK modulation scheme communication may be carried out. For example,in case of using a light-emitting diode in visible light communication,in case the bit value configuring the binary sequence format informationis equal to 1, the light-emitting diode is turned on, and, in case thebit value is equal to 0, the light-emitting diode is turned off. Thus,the light-emitting diode may be turned on and off (i.e., flicker). Asthe receiving device receives and recovers the data being transmitted inthe form of visible light in accordance with the above-described on andoff state (or flickering) of the light-emitting diode, the communicationusing visible light may be carried out. However, since the flickering ofthe light-emitting diode cannot be recognized by the human eye, peoplethink and feel that the lighting is continuously maintained in the onstate.

For simplicity in the description, as shown in FIG. 8, information of abinary sequence format having 10 bit values is used in thisspecification. Referring to FIG. 8, information of a binary sequenceformat having a value of ‘1001101011’. As described above, in case thebit value is equal to 1, the transmitting device is turned on, and, incase the bit value is equal to 0, the transmitting device is turned off.Accordingly, among the 10 bit values, the symbols are turned on in 6 bitvalues. In this case, given that 100% of the consumed power is used whenall of the symbols are turned on in all of the 10 bit values, and, incase a duty cycle shown in FIG. 8 is followed, the consumed power is60%.

More specifically, it may be said that the consumed power of thetransmitter is determined in accordance with a ratio between 1 s and 0 sconfiguring the binary sequence format information. In other words, incase there is a constraint condition specifying that the consumed powerof the transmitter should be maintained at a specific value, the ratiobetween the 1 s and 0 s configuring the binary sequence formatinformation should also be maintained. For example, in case of alighting device, since the lighting should be maintained at a specificluminance value that is wanted by the users, the ratio between the 1 sand 0 s configuring the binary sequence format information should alsobe maintained accordingly.

However, for the wake-up receiver (WUR), since the receiving device isthe subject, the transmission power is not significantly important. Oneof the main reasons for using the OOK is because the amount of consumedpower during the decoding of a received signal is considerably small.Before performing the decoding, the difference between the amount ofconsumed power in the main radio and in the WUR is small. However, asthe decoding process is carried out, the difference in the amount ofconsumed power becomes apparent. The approximate amount of consumedpower is as shown below.

The current Wi-Fi power consumption is approximately 100mW. Morespecifically, power may be consumed as follows: Resonator+Oscillator+PLL(1500 uW)->LPF (300 uW)->ADC (63 uW)->decoding processing (OFDMreceiver) (100 mW).

However, the WUR power consumption is approximately 1 mW. Morespecifically, power may be consumed as follows: Resonator+Oscillator(600 uW)->LPF (300 uW)->ADC(20 uW)->decoding processing (Envelopedetector) (1 uW).

FIG. 9 illustrates a method for designing an OOK pulse according to anexemplary embodiment of this specification.

In order to generate an OOK pulse, an OFDM transmitting device of 802.11may be re-used. The transmitting device may generate a sequence having64 bits by applying 64-point FFT, just as in the legacy 802.11.

The transmitting device should generate the payload of a wake-up packetby performing modulation using the OOK scheme. However, since thewake-up packet is used for low-power communication, the OOK scheme isapplied to the ON-signal. Herein, the ON-signal corresponds to/isrelated with a signal having the actual power value, and an OFF-signalcorresponds to/is related with a signal that does not have an actualpower value. Although the OOK scheme is also applied to the OFF-signal,since the OFF-signal is not a signal that is generated by using thetransmitting device, and, accordingly, since the signal is not actuallytransmitted, the OFF-signal is not considered when generating thewake-up packet.

In the OOK scheme, Information (bit) 1 may correspond to the ON-signal,and Information (bit) 0 may correspond to the OFF-signal. On the otherhand, if the Manchester coding method is applied, it may be indicatedthat Information 1 is shifted from the OFF-signal to the ON-signal, andthat Information 0 is shifted from the ON-signal to the OFF-signal.Conversely, it may also be indicated that Information 1 is shifted fromthe ON-signal to the OFF-signal, and that Information 0 is shifted fromthe OFF-signal to the ON-signal. The Manchester coding method will bedescribed later on in detail.

Referring to FIG. 9, as shown in the right side frequency domain graph(920), the transmitting device selects 13 consecutive subcarriers of thereference band, 20 MHz band, as a sample and applies a sequence. In FIG.9, among the subcarriers of the 20 MHz band, the 13 subcarriers that arelocated in the middle are selected as the sample. More specifically,among the 64 subcarriers, the transmitting device selects subcarriershaving subcarriers indexes ranging from −6 to +6. At this point, sincesubcarrier index 0 is a DC subcarrier, this subcarrier may be nulled as0. A specific sequence is configured only in the sample of the selected13 subcarriers, and all of the remaining subcarriers excluding the 13selected subcarriers (subcarrier indexes ranging from −32 to −7 andsubcarrier indexes ranging from +7 to +31) are set to 0.

Additionally, since subcarrier spacing corresponds to/is related with312.5 KHz, the 13 subcarriers have a channel bandwidth of approximately4.06 MHz. More specifically, it may be understood that, in the 20 MHzband of the frequency domain, power exists only in 4.06 MHz. Thus, asdescribed above, by focusing the power to the center, it will beadvantageous in that a Signal to Noise Ratio (SNR) may be increased, andthat power consumption in an AC/DC converter of the receiving device maybe reduced. Additionally, since the sampling frequency band is reducedto 4.06 MHz, the amount of the consumed power may be reducedaccordingly.

Additionally, as shown in the left side time domain graph (910), thetransmitting device performs 64-point IFFT on the 13 subcarriers, so asto generate one ON-signal in the time domain. One ON-signal has the sizeof 1 bit. More specifically, a sequence being configured of 13subcarriers may correspond to 1 bit. Conversely, the transmitting devicemay bot transmit the OFF-signal at all. By performing IFFT, a symbol of3.2 us may be generated, and, if a cyclic prefix (CP) (0.8 us) isincluded, one symbol having the length of 4 us may be generated. Morespecifically, 1 bit indicating one ON-signal may be loaded in onesymbol.

The reason for configuring and transmitting a bit, as described in theabove-described exemplary embodiment, is to reduce power consumption inthe receiving device by using an envelope detector. Thus, the receivingdevice may decode a packet with a minimum amount of power.

However, a basic data rate for one information may correspond to 125Kbps (8 us) or 62.5 Kbps (16 us).

By generalizing the description presented above, a signal beingtransmitted from the frequency domain is as described below. Morespecifically, each signal having a length of K within the 20 MHz bandmay be transmitted by being loaded in K number of consecutivesubcarriers, among the total of 64 subcarriers. More specifically, as anumber of subcarriers being used for transmitting a signal, the value Kmay correspond to the bandwidth of an OOK pulse. Coefficients ofsubcarriers other than the K number of subcarriers are equal to 0. Atthis point, indexes of the K number of subcarriers being used by asignal corresponding to information 0 and information 1 are the same.For example, a subcarrier index that is being used may be indicated as33-floor(K/2):33+ceil(K/2)-1.

At this point, Information 1 and Information 0 may have the followingvalues.

Information 0=zeros(1,K)

Information 1=alpha*ones(1,K)

The alpha is a power normalization factor and may, for example, be equalto 1/sgrt(K).

FIG. 10 is a descriptive diagram of a Manchester coding method accordingto an exemplary embodiment of this specification.

Manchester coding is a type of line coding that corresponds to/isrelated with a coding method in which a transition in a magnitude valueoccurs at a midpoint of one bit period. And, information of this methodmay be indicated as shown below in the following table.

TABLE 1 Original data Clock Manchester value 0 = 0 XOR 0 1 1 1 0 1 1 0

More specifically, the Manchester coding method (or technique) refers toa method of converting data from 1 to 01 and from 0 to 10 or from 1 to10 and from 0 to 01. Table 1 shows an example of data being convertedfrom 1 to 10 and from 0 to 01 by using Manchester coding.

As shown in FIG. 10, from top to bottom, the drawing illustrates a bitsequence that is to be transmitted, a Manchester coded signal, a clockthat is reproduced by the receiving end, and data that is reproduced bythe clock.

If data is transmitted from the transmitting end by using the Manchestercoding method, the receiving end reads the data after a brief momentbased on a transition point, wherein transition of 1→0 or 0→1 occurs.Then, after recovering the data and recognizing the transition point oftransitioning 1→0 or 0→1 as the transition point of the block, the clockis recovered. Alternatively, when a symbol is divided based on thetransition point, a simple decoding may be performed by comparing thepower level of the front part of the symbol and the power level of theback part of the symbol based on the midpoint of the symbol.

As shown in FIG. 10, the bit sequence that is to be transmittedcorresponds to/is related with 10011101, and the bit sequence that is tobe transmitted being processed with Manchester coding corresponds to/isrelated with 0110100101011001, the clock that is reproduced in thereceiving end recognizes a transition point of the Manchester-codedsignal as the transition point of the block, and, then, data isrecovered by using the clock, which is reproduced as described above.

When using the above-described Manchester coding method, communicationmay be carried out in a synchronization method by using only a datatransmission channel and without using a separate clock.

Additionally, in the above-described, by using only the datatransmission channel, a TXD pin may be used for data transmission, andan RXD pin may be used for data reception. Therefore, a synchronizedtwo-way transmission may be performed.

This specification proposes diverse symbol types that can be used in aWUR and the corresponding data rate.

Since STAs requiring robust performance (or capacity) and STAs receivingintense signals from an AP are intermixed, depending upon the situation,supporting an efficient data rate is needed. In order to achieve areliable and robust performance, a symbol-based Manchester coding methodand a symbol repetition method may be used. Additionally, in order toachieve a high data rate, a symbol reduction method may be used.

At this point, each symbol may be generated by using the legacy 802.11OFDM transmitter. And, the number of subcarriers that are used forgenerating each symbol may be equal to 13. However, the number ofsubcarriers will not be limited only to this.

Additionally, each symbol may use OOK modulation, which is configured ofan ON-signal and an OFF-signal.

A symbol that is generated for the WUR may be configured of a cyclicprefix (CP) (or a guard interval (GI)) and a signal part indicatingactual information. By diversely configuring the lengths of the CP andthe actual information signal, or by repeating the CP and the actualinformation part, a symbol having diverse data rates may be designed.

Diverse example related to the symbol types are shown below.

For example, a basic WUR symbol may be indicated as CP+3.2 us. Morespecifically, 1 bit is indicated by using a symbol having the samelength as the legacy Wi-Fi. Most particularly, the transmitting deviceperforms IFFT after applying a specific sequence to all of thesubcarriers that are available for usage (e.g., 13 subcarrier), therebyconfiguring an information signal part of 3.2 us. At this point, amongall of the subcarriers that are available for usage, a coefficient of 0may be loaded in a DC subcarrier or middle subcarrier index.

Different sequence may be applied to the subcarriers that are availablefor usage in accordance with a 3.2 us ON-signal and a 3.2 us OFF-signal.The 3.2 us OFF-signal may be generated by applying 0 s to all of thecoefficients.

The CP may select and use a part corresponding having a specific lengthat an end part of the information signal 3.2 us that immediately followsthe CP. At this point, the CP may correspond to 0.4 us or 0.8 us. Thislength corresponds to/is related with the same length as the guardinterval of 802.11ac.

Therefore, a 1-bit information corresponding to one basic WUR symbol maybe indicated as shown below in the following table.

TABLE 2 Information ‘0’ Information ‘1’ 3.2 us OFF-signal 3.2 usON-signal

Table 2 does not separately indicate the CP. Actually, when includingthe CP, CP+3.2 us may indicate one 1-bit information. More specifically,the 3.2 us ON-signal may be regarded as a (CP+3.2 us) ON-signal, and the3.2 us OFF-signal may be regarded as a (CP+3.2 us) OFF-signal.

For example, a symbol having Manchester coding applied thereto may beindicated as CP+1.6 us+CP+1.6 us or CP+1.6 us+1.6 us. The symbol havingManchester coding applied thereto may be generated as described below.

In an OOK transmission using a Wi-Fi transmitting device, the timeperiod used for transmitting one bit (or symbol) excluding the guardinterval of the transmitted signal is equal to 3.2 us. At this point, ifManchester coding is also applied, a shift in the signal size (ormagnitude) should occur in 1.6 us. More specifically, eachsub-information having a length of 1.6 us should be given a value of 0or 1, and the corresponding signal may be configured by using the methoddescribed below.

Information 0->10 (Each may be referred to as sub-information 1 0 orsub-symbol 1 (ON) 0 (OFF).)

First 1.6 us (sub-information 1 or sub-symbol 1): Sub-information 1 maybe given a value of beta*ones(1,K). Herein, the beta indicates/isrelated with a power normalization element and may, for example, beequal to 1/sqrt(ceil(K/2)).

Additionally, in order to generate the symbol having Manchester codingapplied thereto, a specific sequence is applied to all subcarriers thatare available for usage (e.g., 13 subcarriers) in units of 2 spaces.More specifically, each even-number indexed subcarrier of the specificpattern is nulled by using 0. For example, when it is assumed that anON-signal is configured by using 13 subcarriers, the specific sequencehaving a coefficient at an interval of 2 spaces may correspond to{a0b0c0d0e0f0g}, {0a0b0c0d0e0f0},or {a0b 0c000d0e0f}. At this point, a,b, c, d, e, f, g may correspond to 1 or −1.

More specifically, among the 64 subcarriers, the transmitting devicemaps the specific sequence to K number of consecutive subcarriers (e.g.,33-floor(K/2) : 33+ceil(K/2)-1) and sets a coefficient of 0 for theremaining subcarriers. Thereafter, the transmitting device performsIFFT. Thus, a time domain signal may be generated. Since the time domainsignals has coefficients existing at an interval of 2 spaces within thefrequency domain, the time domain signal corresponds to/is related witha 3.2 us-length signal of having a cycle of 1.6 us. One of a first 1.6us-cycle signal and a second 1.6 us-cycle signal may be selected andused as sub-information 1.

Second 1.6 us (sub-information 0 or sub-symbol 0): Sub-information 0 maybe given a value of zeros(1,K). Similarly, among the 64 subcarriers, thetransmitting device maps the specific sequence to K number ofconsecutive subcarriers (e.g., 33-floor(K/2) : 33+ceil(K/2)-1) andperforms IFFT, thereby generating a time domain signal. Sub-information0 may correspond to a 1.6 us OFF-signal. The 1.6 us OFF-signal may begenerated by setting all of the coefficients to 0.

One of a first 1.6 us-cycle signal and a second 1.6 us-cycle signal ofthe time domain may be selected and used as sub-information 0. Simply,zero signals (1,32) may also be used as sub-information 0.

Information 1->0 1(Each may be referred to as sub-information ‘0’, ‘1’or sub-symbol 0 (OFF) 1 (ON).)

Since Information 1 is also divided into a first 1.6 us (sub-information0) and a second 1.6 us (sub-information 1), a signal corresponding toeach sub-information may be configured by using the same method as themethod for generating Information 0.

When performing the method for generating Information 0 and Information1 by using Manchester coding, a consecutive occurrence of OFF-symbolsmay be prevented as compared to the legacy method. Accordingly, aproblem of coexistence with the legacy Wi-Fi device does not occur. Theproblem of coexistence refers to a problem that occurs when anotherdevice transmits a signal after determining that the channel is in achannel idle state, due to the existence of consecutive OFF-symbols. Ifthe OOK modulation is only used, the sequence may, for example,correspond to 100001, wherein the OFF-symbol occurs consecutively.However, if Manchester coding is used, the sequence may correspond to100101010110, wherein the OFF-symbols cannot be consecutive.

According to the description provided above, the sub-information may bereferred to as a 1.6 us information signal. The 1.6 us informationsignal may correspond to a 1.6 us ON-signal or a 1.6 OFF-signal. The 1.6us ON-signal and the 1.6 OFF-signal may have different sequences appliedthereto in each subcarrier.

The CP may select and use a part corresponding having a specific lengthat an end part of the information signal 1.6 us that immediately followsthe CP. At this point, the CP may correspond to 0.4 us or 0.8 us. Thislength corresponds to/is related with the same length as the guardinterval of 802.11ac.

Therefore, a 1-bit information corresponding to a symbol havingManchester coding applied thereto may be indicated as shown below in thefollowing table.

TABLE 3 Information ‘0’ Information ‘1’ 1.6 us ON-signal + 1.6 1.6 usOFF-signal + 1.6 us OFF-signal us ON-signal or 1.6 us OFF-signal + 1.6or 1.6 us ON-signal + 1.6 us ON-signal us OFF-signal

Table 3 does not separately indicate the CP. Actually, when includingthe CP, CP+1.6 us+CP+1.6 us or CP+1.6 us+1.6 us may indicate one 1-bitinformation. More specifically, in case of the former structure, the 1.6us ON-signal and the 1.6 us OFF-signal may be respectively regarded as a(CP+1.6 us) ON-signal and a (CP+1.6 us) OFF-signal.

FIG. 11 illustrates an example of inserting a CP in a symbol adoptingManchester coding according to an exemplary embodiment of thisspecification. FIG. 12 illustrates another example of inserting a CP ina symbol adopting Manchester coding according to an exemplary embodimentof this specification.

A CP (or guard interval) may be inserted in a symbol having Manchestercoding applied thereto and, thus, a signal may be transmitted. 4different options for the configuration or insertion of the CP may beproposed.

Option 1: As shown in FIG. 11, a CP (1110, 1120) of 0.8 us may beinserted in a foremost part of the signal. The CP may be inserted byusing a last 0.8 us signal within the time domain signal of the firstsub-information or the second sub-information. According to FIG. 11, theCP (1110) being positioned at the foremost part of the signal isconfigured by using a last 0.8 us signal of the first sub-informationwithin Information 0. The CP (1120) being positioned at the foremostpart of the signal is configured by using a last 0.8 us signal of thefirst sub-information within Information 1.

Option 2: As shown in FIG. 12, a CP (1210, 1220, 1230, 1240) of 0.4 usmay be inserted in front of each sub-symbol. The CP may use a last 0.4us signal of each sub-symbol. According to FIG. 12, the CP (1210) beingpositioned in front of the first sub-information is configured by usinga last 0.4 us signal of the first sub-information within Information 0.Additionally, the CP (1220) being positioned in front of the secondsub-information is configured by using a last 0.4 us signal of thesecond sub-information within Information 0. The CP (1230) beingpositioned in front of the first sub-information is configured by usinga last 0.4 us signal of the first sub-information within Information 1.Finally, the CP (1240) being positioned in front of the secondsub-information is configured by using a last 0.4 us signal of thesecond sub-information within Information 1

Option 3: The same 0.8 us-length CP (or guard interval) as the legacymethod may be used in front of each sub-information. Accordingly, theactual length of one symbol is equal to 4.8 us. Thus, this option isdisadvantageous in that the overhead is increased by 0.8 us as comparedto the legacy method.

Option 4: Each sub-information may be used to have the same length asone symbol. More specifically, since each sub-symbol is used as 0.8 us(CP or guard interval)+3.2 us, the actual length may be equal to Bus.Accordingly, this option is disadvantageous in that the overhead isincreased to twice its initial size as compared to the legacy method.

In Option 3 and Option 4, although the overhead increases as describedabove, Option 3 and Option 4 are advantageous for further enhancing theeffect of reducing Inter Symbol Interference (ISI).

Hereinafter, a method of decoding a signal, by a receiving device, beingtransmitted from a transmitting device after applying Manchester codingwill be described in detail.

The transmitted signal may correspond to a wake-up packet, and a methodfor decoding the wake-up packet may be broadly divided into twodifferent types. A first type corresponds to/is related with anon-coherent detection method, and a second type corresponds to/isrelated with a coherent detection method. The non-coherent detectionmethod refers to a method wherein a phase relation between signals ofthe transmitting device and the receiving device is not fixed.Therefore, the receiving device is not required to measure and adjustthe phase of the received signal. Conversely, in the coherent detectionmethod, the phase between the signals of the transmitting device and thereceiving device is required to be matched.

The receiving device includes the above-described low-power wake-upreceiver. In order to reduce power consumption, the low-power wake-upreceiver may decode a packet (wake-up packet), which is transmitted byusing the OOK modulation scheme, by using an envelope detector.

The envelope detector uses a method of decoding a received signal bymeasuring the power or magnitude of the corresponding signal. Thereceiving device determines in advance a threshold value based on thepower or magnitude of the received signal, which is measured by usingthe envelope detector. Thereafter, when the receiving device decodes thesymbol having OOK applied thereto, if the symbol is greater than orequal to the threshold value, the symbol is determined as Information 1,and, if the symbol is smaller than the threshold value, the symbol isdetermined as Information 0.

A method for decoding a symbol having Manchester coding applied theretois as described below. The receiving device sorts the received signal toa signal corresponding to each bit (or symbol). Then, the receivingdevice calculates a norm value or power of a signal corresponding toeach sub-information and estimates the transmitted information aftercomparing the calculated norm value or power. For example, if the normvalue or power of a signal corresponding to the first sub-information isgreater than the norm value or power of a signal corresponding to thesecond sub-information, the transmitted information may be determined asInformation 0 (i.e., sub-information 1 0). Conversely, if the norm valueor power of a signal corresponding to the first sub-information issmaller than the norm value or power of a signal corresponding to thesecond sub-information, the transmitted information may be determined asInformation 1 (i.e., sub-information 0 1). The norm value indicates/isrelated with a magnitude (or size) scale of a vector. Herein, the normvalue may correspond to a magnitude scale of a signal.

Additionally, without considering channel influence, the decoding may beperformed by simply comparing the norm values or power. Morespecifically, the receiving device knows the power information that isactually transmitted from the transmitting device. Therefore, thereceiving device may determine the transmitted information by simplycomparing the power or norm value of the first sub-information with thepower or norm value of the second sub-information. However, since thechannel situation is not considered in this method, this may result in aconsiderable degradation in the actual performance (or capacity).

As described above, in addition to Manchester coding, even in caseswhere line coding of a similar group is applied, the transmitting devicegenerates a signal corresponding to the sub-information and may thenapply a guard interval (or CP). Additionally, the receiving device mayperform decoding by simply comparing the norm value or power of thereceived signals.

FIG. 13 is a flow chart showing a procedure of transmitting a signalafter applying the OOK scheme and Manchester coding according to anexemplary embodiment of this specification.

The example of FIG. 13 is performed by a transmitting device. And, areceiving device may correspond to a low-power wake-up receiver, and thetransmitting device may correspond to an AP.

Firstly, the terms will be defined. An ON-signal may correspond to asignal having an actual power value. An OFF-signal may correspond to asignal that does not have an actual power value. A first information maycorrespond to Information 0, and a second information may correspond toInformation 1.

In step S1310, the transmitting device generates a wake-up packet.

In step S1320, the transmitting device transmits the wake-up packet tothe receiving device.

The generation process of the wake-up packet will hereinafter bedescribed in detail.

An On-Off Keying (OOK) scheme and Manchester coding are applied in thewake-up packet. Accordingly, the wake-up packet includes a sequencebeing configured of the first information and the second information.

The first information and the second information are configured of anON-signal and an OFF-signal. More specifically, the first informationmay be configured in an order of an ON-signal and an OFF-signal. And,the second information may be configured in an order of an OFF-signaland an ON-signal. The ON-signal may indicate 1, and the OFF-signal mayindicate 0. Accordingly, the first information may be indicated as 10,and the second information may be indicated as 01. This indicates/isrelated with that Manchester coding is applied, and, accordingly, atransition in the signal magnitude occurs at a mid-point of a symbol.

In the first information and the second information, the order of theON-signal and the OFF-signal may also be changed. More specifically, thefirst information may be indicated as 01, and the second information maybe indicated as 10. However, the exemplary embodiment of thisspecification is described based on an assumption that the firstinformation indicates/is related with 10, and that the secondinformation indicates/is related with 01.

Additionally, each of the first information and the second informationcorrespond to a 1-bit information.

Additionally, the ON-signal may correspond to a signal given a powervalue of beta*ones(1,K). The OFF-signal may correspond to a signal givena power value of zeros(1,K). The beta is a power normalization factor.More specifically, the transmitting device may know, in advance, thepower values of the ON-signal and the OFF-signal and may configure thefirst information and the second information accordingly. By using anenvelope detector for decoding the first information and the secondinformation, the receiving device may reduce the amount of power that isconsumed when performing the decoding process.

The ON-signal is transmitted through a first symbol, which is generatedby applying a first sequence on K number of consecutive subcarriers of a20 MHz band and by performing 64-point Inverse Fast Fourier Transform(IFFT). More specifically, the ON-signal may be transmitted through asymbol, which is generated by performing IFFT on one bit. At this point,K is an integer.

In the first sequence, one of a subcarrier having an even-numberedsubcarrier index and a subcarrier having an odd-numbered subcarrierindex is nulled. More specifically, if a subcarrier having aneven-numbered subcarrier index is nulled in the first sequence, thesubcarrier having an odd-numbered subcarrier index may have acoefficient of 1 or −1. More specifically, the subcarrier having theodd-numbered subcarrier index may have a coefficient.

Alternatively, if a subcarrier having an odd-numbered subcarrier indexis nulled in the first sequence, the subcarrier having an even-numberedsubcarrier index may have a coefficient of 1 or −1. More specifically,the subcarrier having the even-numbered subcarrier index may have acoefficient.

More specifically, in the first sequence, a coefficient may exist at aninterval of two spaces of subcarrier indexes.

Additionally, the OFF-signal may be transmitted through a second symbol,which is generated by applying a second sequence to K number ofconsecutive subcarriers of a 20 MHz band and by performing 64-pointIFFT. In the second sequence, the coefficients of all subcarriers areset to 0.

The K number of subcarriers may correspond to a partial band of the 20MHz band. For example, when it is assumed that K=13, and that 20 MHzcorresponds to/is related with the reference band, even though 64subcarriers (or bit sequences) may be used, only 13 subcarriers aresampled and processed with IFFT. Accordingly, the 13 subcarriers maycorrespond to approximately 4.06 MHz. More specifically, a specificsequence (first sequence or second sequence) is configured only in the13 subcarriers, which are selected as a sample, and the remainingsubcarriers excluding the 13 subcarriers are all set to 0. Morespecifically, in the frequency domain, it may be understood that thepower exists for only 4.06 MHz of the 20 MHz band.

Additionally, the subcarrier spacing between each of the K number ofsubcarriers may correspond to 312.5 KHz.

Since the transmitting device performs IFFT after applying a firstsequence having a coefficient at an interval of two subcarrier indexspaces to K number of subcarriers, a 3.2 us-length signal having a cycleof 1.6 us is generated. Accordingly, each of the first symbol and thesecond symbol may have a length of 1.6 us. More specifically, each ofthe first symbol and the second symbol may correspond to a sub-symbol ofa symbol, which is generated by performing IFFT.

Moreover, by inserting a cyclic prefix (CP) in front of each symbol, theoccurrence of Inter Symbol Interference (ISI) may be reduced orprevented.

For example, the first information may be transmitted by having a firstcyclic prefix (CP) inserted only in front of the first symbol.Alternatively, the first information may be transmitted by having asecond CP inserted in front of the first symbol and a third CP insertedin front of the second symbol. Herein, the first CP may have length of0.8 us, and the second CP and the third CP may each have a length of 0.4us. More specifically, in the former case, a long CP is inserted isinserted in the foremost part of the signal, and, in the latter case,short CPs are inserted at the front and in the middle of the signal(i.e., a short CP is inserted in front of each sub-symbol). The formercase is effective in case the influence of the ISI is large at theforemost part of the signal, and the latter case is effective in casethe influence of the ISI also exists in the mid-portion of the signal.

As another example, the second information may be transmitted by havinga first CP inserted only in front of the second symbol. Alternatively,the second information may be transmitted by having a second CP insertedin front of the second symbol and a third CP inserted in front of thefirst symbol. Herein, the first CP may have length of 0.8 us, and thesecond CP and the third CP may each have a length of 0.4 us. Similarly,in the former case, a long CP is inserted is inserted in the foremostpart of the signal, and, in the latter case, short CPs are inserted atthe front and in the middle of the signal (i.e., a short CP is insertedin front of each sub-symbol). The former case is effective in case theinfluence of the ISI is large at the foremost part of the signal, andthe latter case is effective in case the influence of the ISI alsoexists in the mid-portion of the signal.

As yet another example, the first information may be transmitted byhaving a first CP inserted in front of the first symbol and a second CPinserted in front of the second symbol. The second information may betransmitted by having the first CP inserted in front of the secondsymbol and the second CP inserted in front of the first symbol. Each ofthe first CP and the second CP may have a length of 0.8 us. According tothe above-described exemplary embodiment, a long CP may be inserted infront of each sub-symbol, thereby enhancing the effect of reducing theISI.

FIG. 14 is a block view illustrating a wireless device to which theexemplary embodiment of the present invention can be applied.

Referring to FIG. 14, as an STA that can implement the above-describedexemplary embodiment, the wireless device may correspond to an AP or anon-AP station (STA). The wireless device may correspond to theabove-described user or may correspond to a transmitting devicetransmitting a signal to the user.

The AP (1400) includes a processor (1410), a memory (1420), and a radiofrequency (RF) unit (1430).

The RF unit (1430) is connected to the processor (1410), thereby beingcapable of transmitting and/or receiving radio signals.

The processor (1410) implements the functions, processes, and/or methodsproposed in the present invention. For example, the processor (1410) maybe implemented to perform the operations according to theabove-described exemplary embodiments of the present invention. Morespecifically, among the operations that are disclosed in the exemplaryembodiments of FIG. 1 to FIG. 13, the processor (1410) may perform theoperations that may be performed by the AP.

The non-AP STA (1450) includes a processor (1460), a memory (1470), anda radio frequency (RF) unit (1480).

The RF unit (1480) is connected to the processor (1460), thereby beingcapable of transmitting and/or receiving radio signals.

The processor (1460) implements the functions, processes, and/or methodsproposed in the present invention. For example, the processor (1460) maybe implemented to perform the operations of the non-AP STA according tothe above-described exemplary embodiments of the present invention. Theprocessor may perform the operations of the non-AP STA, which aredisclosed in the exemplary embodiments of FIG. 1 to FIG. 13.

The processor (1410, 1460) may include an application-specificintegrated circuit (ASIC), another chip set, a logical circuit, a dataprocessing device, and/or a converter converting a baseband signal and aradio signal to and from one another. The memory (1420, 1470) mayinclude a read-only memory (ROM), a random access memory (RAM), a flashmemory, a memory card, a storage medium, and/or another storage device.The RF unit (1430, 1480) may include one or more antennas transmittingand/or receiving radio signals.

When the exemplary embodiment is implemented as software, theabove-described method may be implemented as a module (process,function, and so on) performing the above-described functions. Themodule may be stored in the memory (1420, 1470) and may be executed bythe processor (1410, 1460). The memory (1420, 1470) may be locatedinside or outside of the processor (1410, 1460) and may be connected tothe processor (1410, 1460) through a diversity of well-known means.

1. A method for transmitting a wake-up packet in a wireless LAN system,comprising: generating, by a transmitting device, the wake-up packet;and transmitting, by the transmitting device, the wake-up packet to areceiving device, wherein an On-Off Keying (OOK) scheme and Manchestercoding are applied to the wake-up packet, wherein the wake-up packetincludes a first information and a second information, wherein the firstinformation and the second information are configured of an ON-signaland an OFF-signal, wherein the ON-signal is transferred through a firstsymbol being generated by applying a first sequence to 13 consecutivesubcarriers within a 20 MHz band and performing 64-point Inverse FastFourier Transform (IFFT), and wherein subcarriers having an odd-numberedsubcarrier index among the 13 consecutive subcarriers are nulled in thefirst sequence.
 2. The method of claim 1, wherein the first informationis configured in an order of the ON-signal and the OFF-signal, andwherein the second information is configured in an order of theOFF-signal and the ON-signal.
 3. The method of claim 2, wherein theON-signal is related with a bit 1, and wherein the OFF-signal is relatedwith a bit
 0. 4. The method of claim 3, wherein the ON-signal is relatedwith a signal having a power value of beta*ones(1,K), wherein theOFF-signal is related with a signal having a power value of zeros(1,K),and wherein the beta is a power normalization factor.
 5. The method ofclaim 2, wherein a coefficient of subcarriers having an even-numberedsubcarrier index among the 13 consecutive subcarriers is set to 1 or -1.6. The method of claim 5, wherein the OFF-signal is transferred througha second symbol being generated by applying a second sequence to 13consecutive subcarriers within the 20 MHz band and performing 64-pointIFFT, and, wherein coefficients of all subcarriers are set to 0 in thesecond sequence.
 7. The method of claim 6, wherein 13 consecutivesubcarriers are related with a partial band of the 20 MHz band, whereinsubcarrier spacing for each of the 13 consecutive subcarriers is equalto 312.5 KHz, and wherein the first symbol has a length of 1.6 us andthe second symbol has a length of 1.6 us.
 8. The method of claim 7,wherein the first information is transmitted by having a first cyclicprefix (CP) inserted only in front of the first symbol, or wherein thefirst information is transmitted by having a second CP inserted in frontof the first symbol and a third CP inserted in front of the secondsymbol, wherein the first CP has a length of 0.8 us, and wherein thesecond CP has a length of 0.4 us and the third CP has a length of 0.4us.
 9. The method of claim 7, wherein the second information istransmitted by having a first CP inserted only in front of the secondsymbol, or wherein the second information is transmitted by having asecond CP inserted in front of the second symbol and a third CP insertedin front of the first symbol, wherein the first CP has a length of 0.8us, and wherein the second CP has a length of 0.4 us and the third CPhas a length of 0.4 us.
 10. The method of claim 7, wherein the firstinformation is transmitted by having a first CP inserted in front of thefirst symbol and a second CP inserted in front of the second symbol,wherein the second information is transmitted by having the first CPinserted in front of the second symbol and the second CP inserted infront of the first symbol, and wherein the first CP has a length of 0.8us and the second CP has a length of 0.8 us.
 11. A transmitting devicefor transmitting a wake-up packet in a wireless LAN system, comprising:a radio frequency (RF) unit transmitting or receiving radio signals; anda processor controlling the RF unit, wherein the processor: generatesthe wake-up packet, and transmits the wake-up packet to a receivingdevice, wherein an On-Off Keying (OOK) scheme and Manchester coding areapplied to the wake-up packet, wherein the wake-up packet includes afirst information and a second information, wherein the firstinformation and the second information are configured of an ON-signaland an OFF-signal, wherein the ON-signal is transferred through a firstsymbol being generated by applying a first sequence to 13 consecutivesubcarriers within a 20 MHz band and performing 64-point Inverse FastFourier Transform (IFFT), and wherein subcarriers having an odd-numberedsubcarrier index among the 13 consecutive subcarriers are is nulled inthe first sequence.
 12. The device of claim 11, wherein the firstinformation is configured in an order of the ON-signal and theOFF-signal, and wherein the second information is configured in an orderof the OFF-signal and the ON-signal.
 13. The device of claim 12, whereinthe ON-signal is related with a bit 1, and wherein the OFF-signal isrelated with a bit
 0. 14. The device of claim 13, wherein the ON-signalis related with a signal having a power value of beta*ones(1,K), whereinthe OFF-signal is related with a signal having a power value ofzeros(1,K), and wherein the beta is a power normalization factor. 15.The device of claim 12, wherein a coefficient of subcarriers having aneven-numbered subcarrier index among the 13 consecutive subcarriers isset to 1 or −1.
 16. The device of claim 15, wherein the OFF-signal istransferred through a second symbol being generated by applying a secondsequence to 13 consecutive subcarriers within the 20 MHz band andperforming 64-point IFFT, and, wherein coefficients of all subcarriersare set to 0 in the second sequence.
 17. The device of claim 16, whereinthe 13 consecutive subcarriers are related with a partial band of the 20MHz band, wherein subcarrier spacing for each of the 13 consecutivesubcarriers is equal to 312.5KHz, and wherein the first symbol has alength of 1.6 us and the second symbol has a length of 1.6 us.
 18. Thedevice of claim 17, wherein the first information is transmitted byhaving a first cyclic prefix (CP) inserted only in front of the firstsymbol, or wherein the first information is transmitted by having asecond CP inserted in front of the first symbol and a third CP insertedin front of the second symbol, wherein the first CP has a length of 0.8us, and wherein the second CP has a length of 1.6 us and the third CPhas a length of 0.4 us.
 19. The device of claim 17, wherein the secondinformation is transmitted by having a first CP inserted only in frontof the second symbol, or wherein the second information is transmittedby having a second CP inserted in front of the second symbol and a thirdCP inserted in front of the first symbol, wherein the first CP has alength of 0.8 us, and wherein the second CP has a length of 1.6 us andthe third CP has a length of 0.4 us.
 20. The device of claim 17, whereinthe first information is transmitted by having a first CP inserted infront of the first symbol and a second CP inserted in front of thesecond symbol, wherein the second information is transmitted by havingthe first CP inserted in front of the second symbol and the second CPinserted in front of the first symbol, and wherein the first CP has alength of 1.6 us and the second CP has a length of 0.8 us.